This is a funny read, since Zildjian sticks are made by Vic Firth (have been for the past 3 years or so) and the Vic Grips and Dip Sticks are the exact same thing, apart for the choice of colors. Look at a Zildjian 5B Dip Stick and a VF Gavin Harrison model. Exact same purple coating.
This is why Colaiuta's switch to VF was predictable. The only thing to change for him is the stamp on his sticks. The reason people experience Zildjian sticks as being less durable has a lot to do with the fact that most Zildjian models have a much thinner neck and taper. Compare a VF 5B to a Zildjian 5B and you'll see what I mean. Even though production has moved to the VF facilities, Zildjian kept their exact model specs (because they do in fact play great).
However, older Zildjian sticks were indeed of notoriously inferior quality.

The Zildjian Dip and Vic Grip have next to nothing in common other than their manufacturers. I can play with Vic Grip all day and it feels great. An hour with Zildjian Dip and I have blisters forming on my fingers. The Dip separates from the stick far easier than Vic Grip ever has.

Sorry, seems like it should be true, but in my experience, it simply isn't. And I have tried both pre-merger and post-merger.